The present invention relates to a photosensitive composition suitable for use as photoresist in a method of manufacturing semiconductor devices and a method of forming a pattern using the composition. 2. Description of the Related Art
Photoresist is used widely in micro-fabrication of electronic devices, such as semiconductor ICs including LSIs. To impart more functions and a higher integration density to an electronic device, it is necessary to form fine resist patterns.
Resist patterns can be formed by means of a reduction-type projecting mask aligner generally known as "stepper." The light source of the mask aligner can be a g-line (436 nm) of a mercury lamp, an h-line (405 run) of a mercury lamp, an i-line (365 nm) of a mercury lamp, an XeF (351 nm) excimer laser, an XeCl (308 nm) excimer laser, a KrF (248 nm) excimer laser, a KrCl (222 run) excimer laser, an ArF (193 nm) excimer laser, an F.sub.2 (157 nm) excimer laser, or the like. The rays emitted from the radiation source are applied to a layer of photoresist, thereby to form a resist pattern. For the microfabricaton, it is necessary to use short wave length radiation, such as excimer or high energy electron beam. Hence, it is greatly demanded that a photoresist be developed which is sensitive to ultraviolet rays of short wavelengths emitted by an excimer laser.
An electron beam and an ion beam, either having a short wavelength, can also be applied to a photoresist layer, thereby to form fine resist patterns. Use of an electron beam or an ion beam is advantageous for enabling to form a resist pattern directly, because the beam can be scanned on a photoresist layer under computer control. It is also demanded that a photoresist be developed which is sensitive to an electron beam and an ion beam.
Two types of resists are known which are sensitive to an excimer laser beam and an electron beam. The first type comprises an azide-series photosensitizer and an acrylic polymer such as polymethacrylate (PMMA) or polyglutarmaleimide (PGMI). The second type comprises an azide-series photosensitizer and a polymer having phenol. The resist of the first type is neither sufficiently sensitive to an excimer laser beam and an electron beam nor sufficiently resistant to dry etching. Although the resist of the second type is adequately resistant to dry etching, a resist pattern formed of it have a cross section shaped like an inverted triangle, and the exposure step and the development step must be performed under precise control.
The recent trend is that the width of the thinnest part of a resist pattern is reduced. This trend raises problems in various methods of exposing resist layers to light. In the case where a resist layer formed on a semiconductor substrate is exposed to light, the reflected light from any stepped portion of the substrate interfere, much affecting the dimensional precision of the resultant resist pattern. In the case where a resist layer is exposed to an electron beam, proximity effect develops due to back scattering of electrons, making it impossible for any part of the resultant resist pattern to have a great height-to-width ratio.
To solve the problems inherent in the above-described resist-patterning processes (hereinafter referred to as "single-layer resist process," so-called "multi-layer resist process" has been developed. This process is briefly described in Solid State Technology, 74 (1981). Further, many studies of resist process have been made and published in the form of theses. Various multi-layer resist processes have been invented. Of these processes, the most commonly tried at present is three-layer resist process using a three-layered resist system. The system comprises a lower layer, an intermediate layer, and an upper layer. The lower layer has a flat upper surface even if the underlying substrate has a rough upper surface, and prevents light reflection from the substrate. The intermediate layer functions as a mask during etching of the lower layer. The upper layer functions as photosensitive one.
The three-layer resist process is advantageous in that it can form a resist pattern more finely than one formed by the single-layer resist process. The process is disadvantageous, however, in that more steps need to be performed than the single-layer resist process. More precisely, many steps must be carried out to form the three-layered resist so that the upper layer is sensitive to an ultraviolet ray having a short wavelength and an ionizing radiation, and the intermediate layer is resistant to dry etching such as reactive ion etching wherein oxygen plasma is applied. This is because there is neither single-layer resist nor multi-layer resist, wherein one layer is not only sensitive to the ultra-violent ray and the ionizing radiation, but also resistant to dry etching.